It has been estimated that male reproductive dysfunction is the primary factor in up to 40% of infertile couples. This high incidence of male factor infertility has promoted an intense search for reliable means to predict human sperm fertilizing potential in vivo and in vitro. For ethical reasons, scientists and physicians have frequently hesitated to perform direct diagnostic functional assessments; that is, binding of human spermatozoa to intact viable human oocytes has usually been regarded as an inappropriate test system. However, reliable and discriminating prognostic assays are needed to determine which infertile men are likely to achieve fertilization in vitro or impregnate their wives when assisted by artificial insemination (AIH).
Tight of human spermatozoa binding to the human zona pellucida represents the first critical event in gamete interaction leading to fertilization and activation of development. This binding step may provide unique information predictive of ultimate sperm fertilizing potential. Due to species specificity, human spermatozoa will bind firmly to only human zonae pellucida. Overstreet J W, Hembree W C: Penetration of the zona pellucida of nonliving human oocytes by human spermatozoa in vitro. Fertil Steril 27:815, 1976.